The field of art to which this invention is directed is catalysts for hydrogenation of hydrocarbons, and for methanization and oligomerization processes.
Metal catalysts based on Fe, Co, Ni and Cu are already used in hydrogenation of hydrocarbons and in methanization and oligomerization processes. A high specific surface area of the metal is important for the catalyst activity. This is achieved, for example, by means of high metal loading, but this results in relatively large metal crystals. Very small metal crystals are obtained only when using very small quantities of metal on the support. The resulting specific metal surface area is therefore usually less than that of catalysts with a high load and large crystals.
A method of obtaining crystal sizes in the range of &lt;2.5 nm even with loads of, for example, 25 wt % MeO (where Me stands for a ferrous metal or copper) on a support is the hydrolysis precipitation method described by Geus (Prep. Catal. III, 1 (1983)). This process starts with a powdered support suspended in a solution of metal nitrate and urea, for example. By thermal decomposition of the urea, the metal is deposited very homogeneously on the support and forms very small crystals in reduction. In this way, it is possible to obtain a specific metal surface area which is otherwise possible only with a high metal load. The resulting powdered catalyst has the disadvantage that it cannot be processed to yield molded bodies without using large quantities of inorganic binders. However, this greatly reduces the active component content which in turn leads to a definite sacrifice in terms of activity.
There have been attempts to produce molded metal catalysts with a high metal dispersion by means of precipitation on preshaped supports according to the hydrolysis method. Studies in this regard have already been conducted by K. F. de Jong (Prep. Catal V., 385 (1990)), although Mn and Mo were used. SiO.sub.2 beads (diameter up to 1.5 mm) were introduced into a very dilute solution of the metal nitrates and urea and the metals were deposited on them by decomposing the urea. The disadvantage of this method is that only a very low metal load (up to 5%) can be achieved. At higher concentrations, some of the metal is precipitated as Me(OH).sub.2 in the solution. U.S. Pat. No. 3,668,148 describes this process for precipitation of nickel, but it has the disadvantage that half of the starting nickel remains in solution.
USSR Inventor's Certificate A 459,247 discloses a process for producing nickel catalysts for hydrogenation of organic compounds and for fine gas purification, whereby the nickel is precipitated from solutions of nickel salts on suspended silica gel by means of an aqueous ammonium hydroxide solution or ammonium carbonate solution. Precipitation is performed at a temperature of 70.degree. C. to 75.degree. C. and a pH of 5 to 7.5. The precipitate is aged in the mother liquor for 1.5 to 2 hours at 90.degree. C. to 95.degree. C. After filtering, washing and drying, the precipitate is calcined and reduced in a stream of hydrogen. The catalysts have a nickel content of 10 to 50 wt %. The BET surface of the support is between 55 and 300 m.sup.2 /g, and the nickel surface amounts to between 18 and 28 m.sup.2 /g of the catalyst. Although it is stated that the catalysts produced in this way are tablets measuring 5.times.5 mm, no information is provided regarding the strength of these tablets, or how catalyst bodies with an increased strength can be obtained. Furthermore, no information is given regarding the size of the nickel crystals or the pore volume.
French Patent A 2,523,869 describes an oligomerization catalyst based on monovalent nickel on a silicic acid support that is produced by treating the silicic acid support with an aqueous alkali or ammonium salt solution having a pH of more than about 10 and then treating the silicic acid that has been pretreated in this way with an aqueous nickel(II) salt solution at a pH of about 8 in order to replace the alkali or ammonium ions bound by the silicic acid with nickel ions. Then the resulting product is heated to 300.degree. C. to 900.degree. C. and the divalent nickel is reduced to monovalent nickel. Thus, the nickel is not in the form of a metal so no statements can be made regarding the size of the metal crystals.
U.S. Pat. No. 4,716,256 discloses a process for selective hydrogenation of diolefins to monoolefins whereby a catalyst that consists essentially of elemental nickel on an inorganic support is used. The catalyst may contain 1 to 40 wt % metallic nickel, preferably 2 to 20 wt % metallic nickel, with 5 to 10 wt % being most preferred. However, no information is provided regarding the other properties of the catalyst.
European Patent B 307,520 describes a hydrogenation catalyst consisting of an aluminum oxide support material, 0.05 to 1.5 wt % sulfur and 1.0 to 25 wt % nickel. The aluminum oxide support material has a pore volume of 1 to 3 cm.sup.3 /g and a surface area of more than 150 m.sup.2 /g, whereby less than 25% of the total pore volume is formed by pores having a pore diameter of less than 15 nm and more than 60% of the pore volume is formed by pores whose diameter is more than 60 nm. The catalyst may be in the form of pellets, beads, extrudates or irregularly shaped bodies, but no information is given regarding the strength of the catalyst. Furthermore, no information is given regarding the size of the nickel crystals.
U.S. Pat. No. 3,668,148 discloses a process for production of metal catalysts on a particulate support whereby the support particles are suspended in an aqueous solution of a salt of the catalyst metal and a substance that releases hydroxyl ions when heated in aqueous solution. The suspension is heated to a temperature of more than 100.degree. C. in an autoclave, whereupon the particles of the catalyst metal are uniformly deposited on the support particles. The catalyst is reduced in the usual way. A number of catalyst metals are described, and metals of the ferrous group and copper are also mentioned. However, no statements are made regarding the pore volume or the formation of molded bodies.
There is a need to obtain catalysts having a high metal load on porous molded bodies without any loss of metal that would also have sufficient strength and high specific pore volume even without the use of binders.